Merge pull request #34 from thomas-vincent/fix-physio

WIP on JDE ASL physio
Updated
Merge branch 'fix-physio' of https://github.com/pyhrf/pyhrf into fix-physio
Perfusion baseline corrected: mean value of posterior normal distribution was not correct
modified validation test for perfusion baseline variance
Refactor tree_to_cuboid to tree_to_xndarray. Fix it and add docstring
Merge pull request #35 from ainafp/fix-physio

Fix physio
Merge pull request #36 from thomas-vincent/fix-cartesian-eval

Refactor tree_to_cuboid to tree_to_xndarray. Fix it and add docstring
Fix simulation of perfusion baseline to match the prior model